Modern-day sprayable clearcoat materials and pigmented topcoat materials, as well as surfacer materials, are low in solvent, i.e., they contain fewer volatile organic compounds (VOCs) which are emitted into the atmosphere in the course of their application and drying. These environmentally compatible coating compositions include low molar mass binders and curing agents. In the case of a two-component (two-pack) coating composition, curing agents are used which already react at low temperatures with the functional groups of the binder, to form a crosslinked film (normally, polyfunctional isocyanates are used); in the case of one-component (one-pack) coating compositions, curing agents are used which-react only at an elevated temperature (normally melamine resins).
Binders of this kind are frequently low molar mass, hydroxy-functional polyesters or polyacrylates. Nowadays use is already being made additionally of acrylic-modified polyesters or of polyester-modified acrylic resins or of mixtures of these resins with one another or of resins of this kind to which reactive diluents have been added (EP 0 680 977, EP 0 896 991, EP 0 940 415, DE 100 33 512.8). Reactive diluents are organic chemicals which lower the viscosity of the coating composition and react with the curatives.
With all of these attempts at a solution there have to date been disadvantages in terms of application reliability, particularly in the industrial use of pigmented topcoat materials and in the drying of such systems.
Pigmented industrial topcoat materials are presently applied by “air mix” or frequently by “airless” techniques in a high film thickness (at least 120 μm). It is here that the existing binders of low molar mass display significant disadvantages in terms of deaeration and drying rate. One object is therefore to provide binders free of the said disadvantages. In addition, such systems are nowadays required to have paint solids contents (mass fraction of solids) of at least 80% (with an efflux time of 90 s from a 4 mm-cup at 23° C.).
Surprisingly it has been found that the requirements in terms of paint solids content, reliability in air mix and airless application, satisfactory deaeration, and drying rate can be met by polymerizing olefinic monomers (e.g., acrylic monomers and/or styrene monomers) in the presence of specific, low molar mass, “hard”, hydroxyl-containing polyesters, the components being used preferably in amounts such that in the resulting hydroxyl group-containing polymer, there are mass fractions of from 30 to 70% of the polyester and from 70 to 30% of the addition polymer, with particular preference mass fractions of from 40 to 60% of polyester and from 60 to 40% of the addition polymer.
The invention accordingly provides hydroxyl group-containing polymers which comprise moieties of polyesters (i.e. which are free from olefinic unsaturations) and moieties of addition polymers formed from olefinically unsaturated monomers, the polyesters containing units of saturated aliphatic cyclic or polycyclic dihydroxy or polyhydroxy compounds or diepoxy or polyepoxy compounds A, saturated aliphatic cyclic dicarboxylic or polycarboxylic acids B, and, where appropriate, further units derived from branched saturated aliphatic acyclic dihydroxy or polyhydroxy compounds C, from aliphatic saturated linear acyclic dihydroxy or polyhydroxy compounds D which contain at least two hydroxyl groups per molecule, from polyfunctional compounds E, the compounds E being selected from aliphatic saturated linear and branched dicarboxylic acids E1 and from aromatic dicarboxylic and polycarboxylic acids E2 containing at least two carboxyl groups per molecule, and from monofunctional compounds F, the compounds F being selected from monocarboxylic acids, monoalcohols, and monoepoxides, all free from olefinic unsaturation, and the addition polymers containing units of olefinically unsaturated alkyl esters G of aliphatic, linear, branched or cyclic olefinically unsaturated monocarboxylic and/or dicarboxylic acids, especially α, β-unsaturated monocarboxylic acids having from 3 to 10 carbon atoms, preferably from 4 to 7 carbon atoms, it being possible for the alkyl radical to be linear, branched or cyclic and said alkyl radical having preferably from 1 to 20, with particular preference up to 15, and in particular from 2 to 12 carbon atoms, olefinically unsaturated hydroxyalkyl esters H of one of the acids specified under G, the hydroxyalkyl radical being derived from an at least dihydric aliphatic linear, branched or cyclic alcohol having preferably from 2 to 15, with particular preference from 2 to 8, carbon atoms, at least one further olefinically unsaturated monomer I selected from the group consisting of vinylaromatics such as styrene, α-methylstyrene, vinyltoluene, vinyl esters of aliphatic linear, branched or cyclic monocarboxylic acids having in particular from 2 to 20, with particular preference from 3 to 12, carbon atoms, halogenated monomers, such as chlorostyrene, vinyl chloride, vinylidene chloride, unsaturated nitriles such as acrylonitrile and methacrylonitrile, amides or diamides of unsaturated monocarboxylic acids, vinyl ethers and allyl ethers of aliphatic linear, branched or cyclic alcohols having preferably from 1 to 18 carbon atoms, esters of glycidyl alcohol or methylglycidyl alcohol with olefinically unsaturated carboxylic acids, and olefinically unsaturated ketones having in particular from 4 to 21 carbon atoms, and also, where appropriate, carboxylic acids J, selected from the monocarboxylic acids specified under G or from the dicarboxylic acids specified under G in unesterified form or preferably in the form in which they are monoesterified with one of the alkyl radicals specified under G or with one of the hydroxyalkyl radicals specified under H.